1. Field of the Invention
The present invention relates to a linear shuttle motor assembly and a controller for controlling the same, wherein the linear shuttle motor is used for linearly moving a load, such as a print head, at a high speed back and forth between two extremes.
2. Description of the Related Art
Heretofore, some printers employ linear motor assemblies which include a stator made up of permanent magnets, and a rotor made up of coils. The stator is fixedly mounted on a printer housing. The rotor is driven in accordance with the principal of Fleming's left-hand rule. A print head is connected to the rotor so as to move reciprocally with reciprical movement of the rotor. In order to suppress generation of moment in the stationary components but obtain couple, a counter balance is connected to the rotor through a vector force conversion mechanism. The drive force of the rotor is transmitted through the vector force conversion mechanism to the counter balance, to recriprically move the rotor and the counter balance in opposite directions in order to maintain a fixed center of gravity for the overall system.
The conventional linear shuttle motor assembly requires a great deal of thrust, because so much thrust is consumed to move the rotor, the print head, and the counter balance and because so much thrust is wasted as transmission loss in the vector force conversion mechanism. In particular, inertial force must be overcome each time the print head reverses movement direction during its reciprical transport. In order to generate repulsion thrust that overcomes the inertial force, it was required that a reverse drive be operated with a large current, say about 20 Amperes, with a D.C. power source generating 40 volts.
A further disadvantage exists in that the transmission loss at the vector force conversion mechanism increases instantaneously each time the head transport direction is reversed. This high transmission loss causes wearing down of the vector force conversion mechanism by abrasion. In order to relieve such disadvantages, it has been proposed to use repulsion springs or repulsion magnets to weaken inertial force generated at the time when the rotor reverses its direction and to supplement repulsion thrust.